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What does the oxidation states of each element in a compound mean?

  1. Apr 17, 2010 #1
    If I have SO42-, I can figure out that the oxidation state of each O ion is 2- and the sulfur ion must then be 6+. What does this number mean? What does it tell you about the electrons in that molecule?
  2. jcsd
  3. Apr 17, 2010 #2
    Oxidation number is not a physical quantity. It is a tool used to keep track of electrons in reactions. If the oxidation number is increased during a reaction, the atom has electrons taken away from it and vice versa.

    Ox. numbers: +III   +II      0  +III
    Reaction:    Au3+ + 3Fe2+ → Au + 3Fe+3

    In the process of this reaction, a gold ion (Au3+) steals one electron each from three iron ions (Fe+2). This is shown in the change of their oxidation numbers.
  4. Apr 17, 2010 #3
    So the oxidation number of an element at a point in time has no meaning, it is only the change in the number that has meaning?
  5. Apr 17, 2010 #4
    You could put it that way, but you don't have to give so much thought to what the numbers represent so long as you can get the neccesary information from their utilization.

    When I learned about them first, it was as a tool for balancing reactions, since some reactions have to be balanced with respect not to molecules o ions, but with respect to electrons, like the one I posted above. In that sence you are right, the actual alue has no physical meaning. It's kind of like potential energy. The value in question can be anything, but it's change during precesses is well defined.
  6. Apr 17, 2010 #5


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    Staff: Mentor

    Actually every correctly balanced reaction should be balanced both in terms of atoms (to reflect mass conservation) and charges (to reflect charge conservation).
    Last edited by a moderator: Aug 13, 2013
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